Wireless communication systems are well known in the art. Generally, such systems comprise communication stations which transmit and receive wireless communication signals between each other. Typically, base stations are provided which are capable of conducting wireless concurrent communications with a plurality of subscriber stations. In CDMA systems specified by the Third Generation Partnership Project (3GPP), base stations are called Node Bs, subscriber stations are called User Equipments (UEs) and the wireless interface between the Node Bs and UEs is known as the Uu interface. FIG. 1 illustrates a typical 3GPP CDMA system.
The Uu radio interface of a 3GPP system uses Transport Channels (TrCHs) for transfer of user data and signaling between UEs and Node Bs. In 3GPP Time Division Duplex (TDD) communications, TrCH data is conveyed by one or more physical channels defined by mutually exclusive physical resources. TrCH data is transferred in sequential groups of Transport Blocks (TBs) defined as Transport Block Sets (TBSs). Each TBS is transmitted in a given Transmission Time Interval (TTI) which may span a plurality of consecutive system time frames. A typical system time frame is 10 microseconds and TTIs are currently specified as spanning 1, 2, 4 or 8 of such time frames.
FIG. 2a illustrates the processing of TrCHs in TTD mode into a Coded Composite TrCH (CCTrCH) and then into one or more physical channel data streams in accordance with 3GPP TS 25.222 v3.8.0. Starting with the TBS data, Cyclic Redundancy Check (CDC) bits are attached and Transport Block concatenation and Code Block segmentation is performed. Convolution coding or turbo coding is then performed, but in some instances no coding is specified. The steps after coding, include radio frame equalization, a first interleaving, radio frame segmentation and rate matching. The radio frame segmentation divides the data over the number of frames in the specified TTI. The rate matching function operates by means of bit repetition or puncturing and defines the number of bits for each processed TrCH which are thereafter multiplexed to form a CCTrCH data stream.
The processing of the CCTrCH data stream includes bit scrambling, physical channel segmentation, a second interleaving and mapping onto one or more physical channels. The number of physical channels corresponds to the physical channel segmentation. For uplink transmissions, UE to Node B, the maximum number of physical channels for transmission of a CCTrCH is currently specified as two. For downlink transmissions, Node B to UEs, the maximum number of physical channels for transmission of a CCTrCH is currently specified as sixteen. Each physical channel data stream is then spread with a channelization code and modulated for over air transmission on an assigned frequency.
In the reception/decoding of the TrCH data, the processing is essentially reversed by the receiving station. Accordingly, UE and Node B physical reception of TrCHs require knowledge of TrCH processing parameters to reconstruct the TBS data. For each TrCH, a Transport Format Set (TFS) is specified containing a predetermined number of Transport Formats (TFs). Each TF specifies a variety of dynamic parameters, including TB and TBS sizes, and a variety of semi static parameters, including TTI, coding type, coding rate, rate matching parameter and CRC length. The predefined collection of TFSs for the TrCHs of a CCTrCH for a particular frame is denoted as a Transport Format Combination (TFC).
Receiving station processing is facilitated by the transmission of a Transport Format Combination Indicator (TFCI) for a CCTrCH. For each TrCH of a particular CCTrCH, the transmitting station determines a particular TF of the TrCH's TFS which will be in effect for the TTI and identifies that TF by a Transport Format Indicator (TFI). The TFIs of all the TrCHs of the CCTrCH are combined into the TFCI. For example, if two TrCHs, TrCH1 and TrCH2, are multiplexed to form CCTrCH1, and TrCH1 has two possible TFs, TF10 and TF11, in its TFS and TrCH2 has four possible TFs, TF20, TF21, TF22, and TF23, in its TFS, valid TFCIs for CCTrCH1 could include (0,0), (0,1), (1,2) and (1,3), but not necessarily all possible combinations. Reception of (1,2) as the TFCI for CCTrCH1 informs the receiving station that TrCH1 was formatted with TF11 and TrCH2 was formatted with TF21 for the received TTI of CCTrCH1.
3GPP optionally provides for “blind transport format detection” by the receiving station, in which case the receiving station considers the potential valid TFCIs. Where there is only one valid TFCI, that TFCI is used in either case.
In 3GPP, time slot transmissions are made in predefined bursts where the transmitted physical channel data is divided into a beginning time slot portion and an ending time slot portion. A selected midamble is included between the two physical channel data portions. The TFCI is currently specified as transmitted in two parts on either side of the midamble and also between the two physical channel data portions. Two examples from 3GPP TR 25.944 V3.5.0 are illustrated in FIGS. 2b and 2c respectively where the block labeled MA represents the midamble and the block labeled T represents the parts of the TFCI. In second example, FIG. 2c, the CCTrCH is mapped to two physical, but only one physical channel includes the TFCI.
The midamble and TFCI are initially processed and then the results can be used to process the physical channel data. There is a brief period of time between reception of a TFCI and the end of both the time slot and the time frame in which it is received which the inventor has recognized can be efficiently used for processing the TFCI.
In 3GPP TDD mode, for each radio frame and for each CCTrCH with physical channels or channelization codes allocated in the frame, the transmitter (Node B or UE) autonomously determines the number of bits, denoted Ndata, to be transmitted in the frame based on the TFC in effect for the frame. The 3GPP algorithm in accordance with TS 25.222 v4.0.0, part 4.2.7.1 is in pertinent part as follows:                Denote the number of data bits in each physical channel by Up,Sp, where p refers to the sequence number 1≦p≦Pmax of this physical channel, and the second index Sp indicates the spreading factor with the possible values {16, 8, 4, 2, 1}, respectively. For each physical channel, an individual minimum spreading factor Spmin is transmitted by means of the higher layers. Then, for Ndata one of the following values in ascending order can be chosen:{U1,S1min,U1,S1min+U2,S2min,U1,S1min+U2,S2min+ . . . +UPmax,(SPmax)min}        Optionally, if indicated by higher layers for the UL the UE shall vary the spreading factor autonomously, so that Ndata is one of the following values in ascending order:        
      {                                                      U                              1                ,                16                                      ,            …            ⁢                                                  ,                          U                              1                ,                                  S                  ⁢                                                                          ⁢                                      1                    min                                                                        ,                                          U                                  1                  ,                                      S                    ⁢                                                                                  ⁢                                          1                      min                                                                                  +                              U                                  2                  ,                  16                                                      ,            …            ⁢                                                  ,                                          U                                  1                  ,                                      S                    ⁢                                                                                  ⁢                                          1                      min                                                                                  +                                                                                      U                              2                ,                                  S                  ⁢                                                                          ⁢                                      2                    min                                                                        ,            …            ⁢                                                  ,                                          U                                  1                  ,                                      S                    ⁢                                                                                  ⁢                                          1                      min                                                                                  +                              U                                  2                  ,                                      S                    ⁢                                                                                  ⁢                                          2                      min                                                                                  +              …              +                                                                                      U                                                P                  max                                ,                16                                      ,            …            ⁢                                                  ,                                          U                                  1                  ,                                      S                    ⁢                                                                                  ⁢                                          1                      min                                                                                  +                              U                                  2                  ,                                      S                    ⁢                                                                                  ⁢                                          2                      min                                                                                  +              …              +                              U                                                      P                    max                                    ,                                                            (                                              SP                        max                                            )                                        min                                                                                            }                     Ndata,j for the transport format combination j is determined by executing the following algorithm:SET1={Ndata such that        
                    (                              min                          1              ≤              y              ≤              I                                ⁢                      {                          RM              y                        }                          )            ×              N        data              -          PL      ×                        ∑                      x            =            1                    I                ⁢                              RM            x                    ×                      N                          x              ,              j                                ⁢                                          ⁢          is          ⁢                                          ⁢          non          ⁢                                          ⁢          negative                      }                Ndata,j=min SET1        
Implicit in the above is that only a subset of allocated physical channels is transmitted in the frame. The receiver (BS or UE) can exploit the knowledge of transmitted codes (whether from the signaled TFCI or blindly detected) to improve performance.
To use the signaled TFCI to determine the identity of the transmitted codes, two obvious methods can be applied:
1. upon receipt of a TFCI, the inverse of the 3GPP transmission processing algorithms described in TS 25.222 can be used to:                a. determine transport block set size after CRC(s) are appended;        b. determine code block number and size and number of filler bits;        c. determine number of bits after coding;        d. determine size of frame size after equalization (before rate matching); and        e. determine frame size (number of transmitted bits) after rate matching;        
in order to determine the identity of the transmitted codes, or
2. pre-compute and store along with the TFC the identity of the transmitted codes.
The first method requires that computations necessary to determine the identity of the transmitted codes be performed upon receipt of the TFCI, but before other received data in the frame is demodulated. The second method does not require the computation in real time of the identity of transmitted codes but does require storage of the identity of up to 136 transmitted codes for each of up to 1024 TFCs.
The inventor has recognized that a third, non-obvious method can be implemented which entails less processing without the need for pre-computing and storing all of the channelization codes.